The discovery of materials which are superconductors above the liquid nitrogen temperature of 77 K has prompted intensive efforts to discover new materials having even higher superconducting on-set and zero resistance temperatures. Many of the first applications for these new materials having high superconducting critical temperatures; i.e., High T.sub.c materials, will undoubtedly be in the form of thin film devices and high speed interconnects.
Examples of such superconductive materials prepared using metallo-organic deposition techniques are disclosed in the previously filed U.S. Ser. No. 186,627, entitled "Formation of Film Superconductors by Metallo-Organic Deposition," assigned to the same assignee of the present application, and herein incorporated by reference. Metallo-organic deposition of the thin films superconductors generally involves a three-step process. First, a metallo-organic solution, such as a composition comprising yttrium, barium, and copper neodecanoates, is spin coated onto a suitable substrate. The metallo-organic film is then cured in air at about 500.degree. C. for about five minutes to pyrolize the metallo-organics, so that all that remains on the substrate surface is a film of metal oxides. Finally, the metal oxide film is rapid thermal annealed at an appropriate temperature to promote recrystallization and grain growth within the film. The resulting films prepared in this manner are characterized by superconductive properties above the liquid nitrogen temperature.
In order to exploit the full potential of the thin films of these and other High T.sub.c superconductive materials, it will be necessary to develop patterning methods capable of delineating fine lines and various geometries from the superconductive materials. Present patterning methods currently include: scribing, wet chemical etching, reactive ion etching, local laser ablation, and ion beam amorphization, as well as others. Patterning methods using focused beam techniques; i.e., ion beam, electron beam and laser beam, wherein the focused beam selectively decomposes a film of metal oxide precursors, are disclosed in U.S. Ser. No. 130,135, entitled "Patterning Thin Film Superconductors Using Focused Beam Techniques," which is assigned to the same assignee of the present application.
During patterning by selective laser pyrolysis, focused laser light is scanned across the surface of a precursor film of suitable metallo-organic material to locally pyrolize the metallo-organic material to its metal oxide. It is important, for proper patterning, that the energy intensity of the beam be sufficiently large to convert enough of the precursor metallo-organic material to its oxide to prevent the pattern lines from being removed during development. The low coefficient of light absorbance of some metallo-organics requires either (1) very intense laser energy to render the organic materials insoluble in the solvent or (2) very thick starting precursor films to be used during the patterning process. The use of intense laser beams is undesirable because damage to underlying films and substrates may result from the intense transmitted laser energy. In many cases, the high power densities results in severe substrate crazing therefore forming lines of defects beneath any subsequently formed superconducting lines. These defects tended to produce electrical discontinuities in the lines or serve as fracture points for the strontium titanate during subsequent annealing. Alternatively, the use of thick precursor films is undesirable because the thick films limit the ultimate resolution of the laser patterning process.
Although there are disadvantages, there are also many advantages to using a focused beam of laser light to selectively pattern and pyrolize the metal oxide precursor films so as to form patterned superconductive thin films. First, laser patterning does not require a vacuum; hence, the entire process of patterning and film formation may be done at ambient pressure. Second, laser patterning is a direct-write process requiring no masking layers for patterning. Lastly, selective pyrolysis of the soft metallo-organic precursors renders only the areas exposed by the laser beam insoluble in their organic solvents. Therefore, the unexposed areas may be removed prior to the subsequent pyrolysis and annealing steps by developing and rinsing away with organic solvents.
Therefore, it is desirable to provide a method for forming patterned films of superconductive materials using focused laser light which does not require intense laser energy or unduly thick precursor films. In addition, as new materials with ever increasing superconductive transition temperatures are sought and developed, it is desirable to have a means for forming patterned thin films of these superconducting materials which utilizes non-vacuum techniques, permits complex patterning configurations and is readily compatible with the new materials.